Imaging systems employing free-radical polymerization to crosslink an energy sensitive composition are well known in the graphic arts and provide, for example, printing plates and photoresists. In order to attain maximum sensitivity, and therefore a higher rate of plate or photoresist production, it is generally necessary to prevent oxygen from inhibiting the polymerization process. This is generally accomplished by the use of a barrier layer topcoat of a material such as polyvinyl alcohol which is relatively impervious to oxygen, the use of an inert or very low pressure atmospheric environment, or the addition of an oxygen scavenger to the energy sensitive composition.
U.S. Pat. No. 4,304,923 discloses printing plate compositions with branched condensation urethane oligomers having both ethylenically unsaturated free-radically polymerizable groups and carboxylic acid groups.
U.S. Pat. No. 3,448,089 describes copolymers suitable for coatings and printing plates containing a plurality of pendant acrylic ester groups and carboxylic acid groups, but they cannot contain peptide groups.
U.S. Pat. Nos. 3,583,950 and 3,598,790 describe copolymers of vinyl azlactones and ethylenically unsaturated monomers. There are no free-radically polymerizable groups in the copolymer.
U.S. Pat. Nos. 4,378,411 and 4,304,705 disclose radiation curable polymers derived from a copolymer of vinyl azlactone having pendant ethylenically unsaturated groups. The polymer does not contain either acid salt groups or quaternary ammonium salt groups attached to it.
U.S. Pat. No. 4,737,560 describes polymer beads derived from polymerization of i) a vinyl azlactone monomer, ii) a water soluble monomer (including acid salt containing monomers), and iii) a cross-linking agent (i.e., a multifunctional free-radically polymerizable monomer). Similarly, U.S. Pat. No. 4,111,922 discloses cross-linked hydrophilic random copolymers derived from quaternary ammonium monomers and ethylenically unsaturated monomers which have improved water absorbency and bacteriostatic properties. In both cases the polymer is an insoluble, uncoatable, cross-linked material and is unsuitable for use in photopolymer imaging.
U.S. Pat. No. 4,451,619 describes a method for modifying the hydrophilicity of alkenyl azlactone derived polymers. The polymers described are not capable of free-radical polymerization crosslinking reactions in that they do not have pendant ethylenically unsaturated groups.
U.S. Pat. No. 4,288,523 describes polymers with pendant acid and peptide groups. In this case the polymer contains no free-radically polymerizable groups.
U.S. Pat. No. 4,914,165 discloses aqueous solvent dispersible, radiation cross-linkable compounds and oligomers containing a polyether backbone and multiple ethylenically unsaturated groups in combination with carboxyl groups. The compounds and oligomers are useful in the graphic arts.
U.S. Pat. No. 4,547,449 discloses liquid electrographic developers which contain an addition copolymer of a quaternary ammonium salt monomer, an acid monomer, and a solubilizing monomer. U.S. Pat. No. 4,199,362 discloses polymer latex compounds derived from copolymerization of acid-containing monomers and ethylenically unsaturated monomers. These compositions do not have free-radically polymerizable pendant groups.
One of the problems encountered with some photosensitive polymer-containing systems is their shelf-lives. Over a period of time of a few days or longer at elevated temperatures or upon natural aging for several months some systems exhibit a significant loss of exposed visible image (EVI), also known in the literature as "printout image", and photospeed. Thus, there is a continued need in the industry for improved photosensitive systems. It was against this background that a search for photosensitive systems with increased shelf-lives and the like was initiated.